source: trunk/doc/src/examples/findfiles.qdoc@ 550

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/*!
    \example dialogs/findfiles
    \title Find Files Example

    The Find Files example shows how to use QProgressDialog to provide
    feedback on the progress of a slow operation. The example also
    shows how to use QFileDialog to facilitate browsing, how to use
    QTextStream's streaming operators to read a file, and how to use
    QTableWidget to provide standard table display facilities for
    applications. In addition, files can be opened using the
    QDesktopServices class.

    \image findfiles-example.png Screenshot of the Find Files example

    With the Find Files application the user can search for files in a
    specified directory, matching a specified file name (using wild
    cards if appropiate) and containing a specified text.

    The user is provided with a \gui Browse option, and the result of
    the search is displayed in a table with the names of the files
    found and their sizes. In addition the application provides a
    total count of the files found.

    \section1 Window Class Definition

    The \c Window class inherits QWidget, and is the main application
    widget. It shows the search options, and displays the search
    results.

    \snippet examples/dialogs/findfiles/window.h 0

    We need two private slots: The \c browse() slot is called whenever
    the user wants to browse for a directory to search in, and the \c
    find() slot is called whenever the user requests a search to be
    performed by pressing the \gui Find button.

    In addition we declare several private functions: We use the \c
    findFiles() function to search for files matching the user's
    specifications, we call the \c showFiles() function to display the
    results, and we use \c createButton(), \c createComboBox() and \c
    createFilesTable() when we are constructing the widget.

    \section1 Window Class Implementation

    In the constructor we first create the application's widgets.

    \snippet examples/dialogs/findfiles/window.cpp 0

    We create the application's buttons using the private \c
    createButton() function. Then we create the comboboxes associated
    with the search specifications, using the private \c
    createComboBox() function. We also create the application's labels
    before we use the private \c createFilesTable() function to create
    the table displaying the search results.

    \snippet examples/dialogs/findfiles/window.cpp 1

    Then we add all the widgets to a main layout using QGridLayout. We
    have, however, put the \c Find and \c Quit buttons and a
    stretchable space in a separate QHBoxLayout first, to make the
    buttons appear in the \c Window widget's bottom right corner.

    \snippet examples/dialogs/findfiles/window.cpp 2

    The \c browse() slot presents a file dialog to the user, using the
    QFileDialog class. QFileDialog enables a user to traverse the file
    system in order to select one or many files or a directory. The
    easiest way to create a QFileDialog is to use the convenience
    static functions.

    Here we use the static QFileDialog::getExistingDirectory()
    function which returns an existing directory selected by the
    user. Then we display the directory in the directory combobox
    using the QComboBox::addItem() function, and updates the current
    index.

    QComboBox::addItem() adds an item to the combobox with the given
    text (if it is not already present in the list), and containing
    the specified userData. The item is appended to the list of
    existing items.

    \snippet examples/dialogs/findfiles/window.cpp 3

    The \c find() slot is called whenever the user requests a new
    search by pressing the \gui Find button.

    First we eliminate any previous search results by setting the
    table widgets row count to zero. Then we retrieve the
    specified file name, text and directory path from the respective
    comboboxes.

    \snippet examples/dialogs/findfiles/window.cpp 4

    We use the directory's path to create a QDir; the QDir class
    provides access to directory structures and their contents. We
    create a list of the files (contained in the newly created QDir)
    that match the specified file name. If the file name is empty
    the list will contain all the files in the directory.

    Then we search through all the files in the list, using the private
    \c findFiles() function, eliminating the ones that don't contain
    the specified text. And finally, we display the results using the
    private \c showFiles() function.

    If the user didn't specify any text, there is no reason to search
    through the files, and we display the results immediately.

    \image findfiles_progress_dialog.png Screenshot of the Progress Dialog

    \snippet examples/dialogs/findfiles/window.cpp 5

    In the private \c findFiles() function we search through a list of
    files, looking for the ones that contain a specified text. This
    can be a very slow operation depending on the number of files as
    well as their sizes. In case there are a large number of files, or
    there exists some large files on the list, we provide a
    QProgressDialog.

    The QProgressDialog class provides feedback on the progress of a
    slow operation. It is used to give the user an indication of how
    long an operation is going to take, and to demonstrate that the
    application has not frozen. It can also give the user an
    opportunity to abort the operation.

    \snippet examples/dialogs/findfiles/window.cpp 6

    We run through the files, one at a time, and for each file we
    update the QProgressDialog value. This property holds the current
    amount of progress made. We also update the progress dialog's
    label.

    Then we call the QCoreApplication::processEvents() function using
    the QApplication object. In this way we interleave the display of
    the progress made with the process of searching through the files
    so the application doesn't appear to be frozen.

    The QApplication class manages the GUI application's control flow
    and main settings. It contains the main event loop, where all
    events from the window system and other sources are processed and
    dispatched. QApplication inherits QCoreApplication.  The
    QCoreApplication::processEvents() function processes all pending
    events according to the specified QEventLoop::ProcessEventFlags
    until there are no more events to process. The default flags are
    QEventLoop::AllEvents.

    \snippet examples/dialogs/findfiles/window.cpp 7

    After updating the QProgressDialog, we create a QFile using the
    QDir::absoluteFilePath() function which returns the absolute path
    name of a file in the directory. We open the file in read-only
    mode, and read one line at a time using QTextStream.

    The QTextStream class provides a convenient interface for reading
    and writing text. Using QTextStream's streaming operators, you can
    conveniently read and write words, lines and numbers.

    For each line we read we check if the QProgressDialog has been
    canceled. If it has, we abort the operation, otherwise we check if
    the line contains the specified text. When we find the text within
    one of the files, we add the file's name to a list of found files
    that contain the specified text, and start searching a new file.

    Finally, we return the list of the files found.

    \snippet examples/dialogs/findfiles/window.cpp 8

    Both the \c findFiles() and \c showFiles() functions are called from
    the \c find() slot. In the \c showFiles() function we run through
    the provided list of file names, adding each file name to the
    first column in the table widget and retrieving the file's size using
    QFile and QFileInfo for the second column.

    We also update the total number of files found.

    \snippet examples/dialogs/findfiles/window.cpp 9

    The private \c createButton() function is called from the
    constructor. We create a QPushButton with the provided text,
    connect it to the provided slot, and return a pointer to the
    button.

    \snippet examples/dialogs/findfiles/window.cpp 10

    The private \c createComboBox() function is also called from the
    contructor. We create a QComboBox with the given text, and make it
    editable.

    When the user enters a new string in an editable combobox, the
    widget may or may not insert it, and it can insert it in several
    locations, depending on the QComboBox::InsertPolicy. The default
    policy is is QComboBox::InsertAtBottom.

    Then we add the provided text to the combobox, and specify the
    widget's size policies, before we return a pointer to the
    combobox.

    \snippet examples/dialogs/findfiles/window.cpp 11

    The private \c createFilesTable() function is called from the
    constructor. In this function we create the QTableWidget that
    will display the search results. We set its horizontal headers and
    their resize mode.

    QTableWidget inherits QTableView which provides a default
    model/view implementation of a table view. The
    QTableView::horizontalHeader() function returns the table view's
    horizontal header as a QHeaderView. The QHeaderView class provides
    a header row or header column for item views, and the
    QHeaderView::setResizeMode() function sets the constraints on how
    the section in the header can be resized.

    Finally, we hide the QTableWidget's vertical headers using the
    QWidget::hide() function, and remove the default grid drawn for
    the table using the QTableView::setShowGrid() function.

    \snippet examples/dialogs/findfiles/window.cpp 12

    The \c openFileOfItem() slot is invoked when the user double
    clicks on a cell in the table. The QDesktopServices::openUrl()
    knows how to open a file given the file name.
*/